Improve horizontal scrolling in the navigation views

Because of QTBUG-3927 the tree views are scrolled completely to the left
when selecting any item because it makes the header column visible. That
is very annoying, because it makes items deep in the hierarchy hardly
readable, even if you manually scrolled horizontally to see them.
Scroll horizontally to make the actual item visible instead.

Task-number: QTCREATORBUG-19204
Change-Id: Ic083236feae8892d210b9d2b1238f3c6b80a8cea
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/libs/utils/navigationtreeview.cpp

@@ -27,6 +27,7 @@
 
 #include <QHeaderView>
 #include <QFocusEvent>
+#include <QScrollBar>
 
 /*!
    \class Utils::NavigationTreeView
@@ -56,6 +57,32 @@ NavigationTreeView::NavigationTreeView(QWidget *parent)
     header()->setStretchLastSection(false);
 }
 
+void NavigationTreeView::scrollTo(const QModelIndex &index, QAbstractItemView::ScrollHint hint)
+{
+    // work around QTBUG-3927
+    QScrollBar *hBar = horizontalScrollBar();
+    int scrollX = hBar->value();
+    const int viewportWidth = viewport()->width();
+    const QRect itemRect = visualRect(index);
+    if (itemRect.x() - indentation() < 0) {
+        // scroll so left edge minus one indent of item is visible
+        scrollX += itemRect.x() - indentation();
+    } else if (itemRect.right() > viewportWidth
+               && (viewportWidth - itemRect.x() < 3 * viewportWidth / 4)) {
+        // If right edge of item is not visible and left edge is "too far right",
+        // then move so it is either fully visible, or to the left edge.
+        // For this move the left edge one indent to the left, so the parent can potentially
+        // still be visible.
+        if (itemRect.width() + indentation() < viewportWidth)
+            scrollX += itemRect.right() - viewportWidth;
+        else
+            scrollX += itemRect.x() - indentation();
+    }
+    scrollX = qBound(hBar->minimum(), scrollX, hBar->maximum());
+    TreeView::scrollTo(index, hint);
+    hBar->setValue(scrollX);
+}
+
 // This is a workaround to stop Qt from redrawing the project tree every
 // time the user opens or closes a menu when it has focus. Would be nicer to
 // fix it in Qt.

src/libs/utils/navigationtreeview.h

@@ -36,6 +36,7 @@ class QTCREATOR_UTILS_EXPORT NavigationTreeView : public TreeView
     Q_OBJECT
 public:
     explicit NavigationTreeView(QWidget *parent = 0);
+    void scrollTo(const QModelIndex &index, ScrollHint hint = EnsureVisible) override;
 
 protected:
     void focusInEvent(QFocusEvent *event) override;